Embodiments of the present invention relate to a wireless power transmission device and a wireless power transmission system.
Wireless power transmission is a technique of wirelessly supplying power to household appliances or electric cars rather than using a power line which is an existing wire. This technique is advantageous in that a device which needs to be supplied with power can be charged wirelessly without connecting the device to a power outlet using a power cable. Thus, research related thereto has been actively conducted.
Wireless power transmission techniques are largely divided into a magnetic induction method, a magnetic resonance method, and a microwave method. The magnetic induction method is a technique using magnetic inductive coupling between adjacent coils. In the magnetic induction method, the distance between two power transmission/reception coils is several centimeters or less and transmission efficiency depends greatly on the arrangement of the two coils. The magnetic resonance method is a technique of transmitting non-radial magnetic-field energy between two separate resonators through resonant coupling. In the magnetic resonance method, wireless power transmission may be performed when the distance between power transmission/reception coils is about 1 to 2 m. The magnetic resonance method is more advantageous than the magnetic induction method, in that an arrangement of two coils is relatively flexible and a range of wireless charging may be extended according to a relay method. The microwave method is a technique of transmitting power by emitting super-high-frequency electromagnetic waves such as microwaves via an antenna. When the microwave method is used, long-distance wireless power transmission can be conducted but a safety problem caused by electromagnetic waves should be considered.
A wireless power transmission system includes a wireless power transmission device which wirelessly transmits power, and a wireless power reception device which wirelessly receives the power. Generally, when the wireless power transmission device and the wireless power reception device have the same resonant frequency, maximum power transmission may occur in the wireless power transmission system.
The resonant frequency may vary according to the distance between the wireless power transmission device and the wireless power reception device or locations of the wireless power transmission device and the wireless power reception device. That is, in order to achieve maximum power transmission in the wireless power transmission system, a condition that the wireless power transmission device and the wireless power reception device should have the same resonant frequency should be satisfied. For example, the distance between the wireless power transmission device and the wireless power reception device should be a specific value or the wireless power transmission device and the wireless power reception device should be located at specific positions. When the distance between the wireless power transmission device and the wireless power reception device or the locations thereof are changed and a condition of transmitting a maximum amount of power from the wireless power transmission device to the wireless power reception device is thus not satisfied, reactive power increases in the wireless power transmission device, thereby decreasing wireless power transmission efficiency.
To solve this problem, Korean laid-open patent application No. 2012-0129821 suggests that power be transmitted by changing a resonance frequency of a wireless power transmission device. However, when the resonant frequency is changed, the amount of power requested by a wireless power reception device cannot be transmitted without changing an external power source.
In a wireless power transmission system including one wireless power transmission device and two or more wireless power reception devices, when the wireless power transmission device wirelessly transmits power to the two or more wireless power reception devices, loads on the wireless power transmission device increases and thus the amount of power to be transmitted to the loads increases.
Various parameters, such as a Q factor of a power transmission coil, a voltage, circuit efficiency, an inductance, etc., of the wireless power transmission device may be changed so that a wireless power transmission device may transmit power requested by a plurality of wireless power reception devices. The Q factor of the power transmission coil among the parameters or the size of power transmission coil should be increased to transmit the requested power to the wireless power reception devices by changing the power transmission coil of the wireless power transmission device. That is, the amount of power to be transmitted from the wireless power transmission device to the wireless power reception devices may be increased by increasing the Q factor or the size of the power transmission coil of the wireless power transmission device.
However, the size of the wireless power transmission device has been determined according to design, consumers' request, or the like and thus increasing the size of the power transmission coil is limited. Furthermore, it is difficult to manufacture a power transmission coil having a Q factor greater than a certain value. Accordingly, a power transmission coil having a high Q factor is expensive and thus manufacturing costs of the wireless power transmission device increase.
Furthermore, since resonance conditions of wireless power reception devices and wireless power transmission devices are different, wireless power transmission optimized for the wireless power reception devices cannot be conducted. Thus, the wireless power transmission devices or the wireless power reception devices may be heated, and exploded in a worst-case scenario.